ABTech Tweeter and the AR-3a

[Rich W]

It's been quite a while since I've posted on CSP, as I've been spending more time concentrating on the electronics restoration side of vintage audio. But everything comes around again, well, you know . . .

Recently, I opened up my restored AR-3a's (again), as the pots were once again getting intermittant, in spite of all the polishing and application of dielectric grease, So I surrender . . . I'm giving up being a purist, and am in the process of installing LPads. Actually, I wasn't being such a purist after all in that several years back, I installed a set of AB Tech tweeters to replace the ageing and rapidly-going-silent original tweeters. I had been pretty happy with them.

Then I saw RoyC post regarding the mechanical changes to the ABTech tweeter he was experimenting with along with Larry Ligace. Of course, being the OCD individual that I am, thinking that there might be just a bit more performance I can squeeze out of my 3a's, I couldn't seal up those cabinets without at least asking some questions.

- The original CSP AR-3a restoration guide suggests the .07 mH shunt inductor, along with installing the ABTech tweeters out-of-phase with respect to the midrange, which is what I did. Roy, your recent post suggest wiring in-phase with a 4 uF rather than 6 uF cap. Both methods obviously address limiting the ABTech's output in the frequency range transitioning from the mid-range. Did you find using the in-phase/smaller cap method more effective in that regard? Did it give a more cohesive sound image?

- I realize the physical enhancements to the ABTech are propietory, but what frequency range were you targeting to mitigate the percieved harshness of the ABTech? Do those changes dovetail with the suggested new crossover changes (in-phase, smaller cap). Do you think I would benefit from changing the crossover without any physical modification to the tweeters?

I have to say, I never felt the ABTech to be harsh, but then again, my room is heavily damped. I had run a set of reverberant field frequency curves for my AR-3a's a few years back (posted on CSP) which seemed quite smooth, even rolled off to match the original 3a (what Allison refers to as the "Concert Hall" slope). But maybe I don't know what I'm missing . . .

Good to be back.

Rich W

[RoyC]

Hi Rich,

The polarity change and reduction in the series cap value are tweaks intended to more closely match the reticent nature of the original tweeter when the ABT tweeter is used with 8 ohm L-pads. (The L-pad lowers the crossover point somewhat and increases output.)

The ABT tweeter, unlike most good tweeters, has no damping material under the dome. The modification consists of the addition of material under the dome to reduce sibilance.

If you (or any forum member) would like to discuss the modification further send me a PM.

The addition of the small inductor, which you have already done, is the most important aspect of adapting the ABT tweeter to the 3a.

Roy

[Carlspeak]

In the past few months I have used the modded ABT tweeter in an AR11 and LST restorations with much success. In my case I used 5 uF cap and shunt 0.1 mH coils. Detail acoustic tests were shared with Roy and Larry.

[Rich W]

Thanks, gentlemen. Roy, I've sent you a PM.

Rich Wilhelm

[RoyC]

Richard,

I just sent you a second PM.

Roy

[RoyC]

In the past few months I have used the modded ABT tweeter in an AR11 and LST restorations with much success. In my case I used 5 uF cap and shunt 0.1 mH coils. Detail acoustic tests were shared with Roy and Larry.

Thanks again for your measurements and observations, Carl. Your massive LST project was also very insightful regarding the behavior of this tweeter.

Roy

[frankmarsi]

8-26-13

AB-Tech tweeter and the AR-LST.

Hi you guys, is it possible that I may be clued in on what was determined with the "massive-LST-project"? I’m just curious, as I sit here with a newly discovered problem.

I’ve observed that one of my newly inoperable woofers has an interesting condition.

Yes, it appears that one of the leads of the woofer has separated at the point where it meets the cone. It broke clear off with the lead dangling from the terminal strip, with the lead appearing undamaged and intact. A clean break I'll tell you!

I thought about it and I’m thinking the paper of the cone would need an especially strong glue to adhere the lead to the cone. I’m afraid the paper might rip or something when worked on, and there appears to be a ball of glue that was attaching the lead to the cone when viewed from the front of the cone. Could I proceed to somehow separate the remnants of glue/soldered lead from the cone without damaging it?

Can some one offer any advice, as I may be able to salvage this ‘long/short’ lead woofer? Which, I still believe offer a bit more bass response than the other types and being a bass-hound that is important for me to keep it alive and well.

Out in my newly settled semi-rural ‘AR-Ville’ area, there’s not much else to do except cut the grass, walk aimlessly through the local walmart and dabble with inane out-back country-ish things.

So, my projected ABT, LST tweeter 'massive-project' is close to being a reality and along with the six AR-3a's a good time is promised to be had by all. Then I will ponder what to do with the 'other' untouched pair of LST's. I could either stack them on top of the four stacked LSTs already in use, or perhaps use them as rear channels or, or, I don't even know what else? Lord knows I ain't gonna sell them, are you kidding me, or what?

fm

P.S. Roy, soon I plan to attempt the ABT tweeter thing but, I’m still curious to hear what you and Carl have learned about using these tweeters in the LSTs.

[RoyC]

Frank,

The ball of glue on the cone is where your broken lead connects to the voice coil lead. That connection needs to be re-soldered if you can manage to expose the ends.

I'll let Carl discuss his LST rebuild if he wishes to. What we learned was what crossover change is needed to make the ABT tweeters sound sufficiently LST-ish. (Carl mentioned the crossover component values he used above.) ALL of the tweeters must be ABT tweeters for it to work.

Roy

[Carlspeak]

I need to make a correction. I used 4 uF cap and 0.1 mH air coils on the ABT tweeters in the LST. IIRC, the 5 uF cap was used in the AR-11 job.

Below is an acoustic test showing a zoomed in portion of the LST with ABT tweeter's response tested with just a 4uF cap and again with the added coil. the other curve is of the midrange. With the coil, the tweeter rolls off sooner in the 5 - 6 kHz range. Equally as important, the 12 dB/octave roll off significantly reduces harmonic distortion.

I've also added a pic of two of the 4 ABT front wired tweeters I installed.

[frankmarsi]

I need to make a correction. I used 4 uF cap and 0.1 mH air coils on the ABT tweeters in the LST. IIRC, the 5 uF cap was used in the AR-11 job.

Below is an acoustic test showing a zoomed in portion of the LST with ABT tweeter's response tested with just a 4uF cap and again with the added coil. the other curve is of the midrange. With the coil, the tweeter rolls off sooner in the 5 - 6 kHz range. Equally as important, the 12 dB/octave roll off significantly reduces harmonic distortion.

I've also added a pic of two of the 4 ABT front wired tweeters I installed.

8/27/13

Hi ya Carl and Roy. Pardon my inability to understand all this stuff.

O.K. let me get this straight. Are you speaking of using only two tweeters in the front as I’ve read in other posts or are we speaking of adding the full complement of four tweeters?

Then are we speaking of adding a separate coil and capacitor to each tweeter and not using a singular coil installed in the actual cross-over? I see you’re speaking of a .1mh coil and 4uf capacitor presently. I believe I bought a load of .5 and .7mh coils as that was determined here a while ago.

I’d like to install all four tweeters at one time, can’t I still go into the crossover itself and simply use one coil?

I’m getting confused more than ever after all these changes in values of components.

I thought it would be better to use one coil directly in the cross-over?

I’m now really confused, but what else is new? Please advise as I'm dealing with a lot of distracting unrelated matters and it's difficult to concentrate.

fm

[Carlspeak]

Frank: You must replace all 4 tweeters to have a balanced sound and have compatability with the new cap and coil needed to match up with the new tweeters. You only need one cap and one coil per speaker. BTW, I hope the picture I showed of the ABT tweeters in an LST didn't confuse you . That was just a close up of the two center ones. ALL 4 tweeters were replaced in that job.

I've recently been in communication with a chap in South Africa who has LST's to restore and his questions are similar to yours. He should be joining the conversation soon as he is a new member.

Below is a picture of the LST I repaired by adding the new ABT tweeters. It shows the back side with the xover exposed. Note the new midrange and tweeter caps. Also note the air coil sitting on the base of the cabinet. It has been wired to the pos. return wired from the tweeters to the rotary switch and the common (neg.) leads.

[RoyC]

8/27/13

I believe I bought a load of .5 and .7mh coils as that was determined here a while ago.

fm

Hopefully not, Frank...

.05 and .07mh inductors (not .5 and .7mh) have been discussed in relation to the ABT tweeter and the HiVi tweeter in other models. The LST and LSTII are more challenging and rare, so we were doing much speculating on those models to this point.

Hmmm...I believe you have been buying loads of parts for some time now. I want to be first in line for your "clearance sale".

Roy

[frankmarsi]

Hopefully not, Frank...

.05 and .07mh inductors (not .5 and .7mh) have been discussed in relation to the ABT tweeter and the HiVi tweeter in other models. The LST and LSTII are more challenging and rare, so we were doing much speculating on those models to this point.

Hmmm...I believe you have been buying loads of parts for some time now. I want to be first in line for your "clearance sale".

Roy

Follow up:

Roy, I have been pretty wild since I've retired! And yes I have bought loads of stuff but not at insane prices as I always hunt for the lowest prices by instinct, I grew-up in New York City!.

And yes, you will be first in line for the big 'clearance-sale' as I feel you deserve to be for putting up with my B.S.

I've got to check to see what I have exactly, whether they're .05 or .5, the former I presume. I bought enough for 4 LSTs as the info coming from CSP was seemingly changing so often regarding the operation.

Since I had to move to Jersey in such a hurried fashion with stuff in cardboard boxes, some stuff in plastic totes, etc. I'm finding it difficult to sort through all of it as it’s all over the place. It’s not easy with all of the speakers, turntables, amps, pre-amps, etc. etc.

I would like to plan a time if and when we could meet, when, I can’t say just yet.

I'd need a guru like yourself to guide me through the deluge. There’s nothing worse than being over-whelmed by oneself.

fm

P.S. In other news regarding my insanity, I've been enjoying the much heralded and economically priced Denon DL-301II, Wow, boy what a musical sounding cartridge. It forced me to buy a Denon AU-320 SUT before I picked it up, and it's the bee'-knees as the expression goes. It really allows the LSTs to sing at their best! With articulate bass, lucious mids, and nicely extended treble are the hallmarks of the SME 3009 non-improved combo that its mounted in, and not the overly done highs as my AT-150MLX can sometimes present. At around 200 bucks, it seemingly out does all of my other cartridges and made me a subscriber of MC cartridges even though there are many other choices and with prices not suited to the common budget like mine.

[Carnivore]

I believe I'm the owner of the "Massive LST Project" speakers. 6 out of the 8 tweeters were dead and the crossovers needed work when I brought them to Carl, so I asked him to take as much time as he needed to get the speakers sounding right with the newly modded ABT tweeters. Thanks again for the outstanding work, Carl.

I’d love to be able to tell everyone how true to the original sound these speakers are with the ABT tweeters, but the fact is they weren’t working when I acquired them and I never owned LSTs before so I don’t have a point of reference for comparison. They seem brighter than I expected but that could be due to my assumption that the LST would be a softer sounding speaker, or it could just be my choice of spectral balance switch position. I happen to like a lively high end so the latter is certainly possible and I don't consider it a bad thing.

In any case I'm quite enjoying them. I think it would be interesting to hear my speakers compared side by side with a pair of well-performing stock LSTs though, just to understand what kind of audible difference the modded ABT tweeters make. If anyone with a pair in the NYC metro wants to get together for such a listening test, let me know and maybe we could report our impressions back to the group. (I'm in north Jersey).

[Carlspeak]

Hi Dan:

You and Frank Marsi should hopefully get together somehow and do some comparative listening sessions. I'm sure Frank would be interested in hearing the ABT modded tweeter in an LST.

Let us know what your collective impressions are.

[frankmarsi]

Frank,

The ball of glue on the cone is where your broken lead connects to the voice coil lead. That connection needs to be re-soldered if you can manage to expose the ends.

I'll let Carl discuss his LST rebuild if he wishes to. What we learned was what crossover change is needed to make the ABT tweeters sound sufficiently LST-ish. (Carl mentioned the crossover component values he used above.) ALL of the tweeters must be ABT tweeters for it to work.

Roy

Roy, Baby, I did deal with it and re-soldered that shot wire without burning the paper cone clear thru, only to to hear from said results that the VC is gone.

Now, if you were in the military in 1968 to 1970 as I was, that would be good news. I didn't and don't wish these memories on anyone. O.K.? Jack? No personal attacks here jack on anyone, we're safe now!

But out of 16-18 spare 12 inch woofers, I only got 10 left, good heavens. I still have to furinsh 6 AR-3a's with new, rebuilt woofers. After that, I'll only have 4 left for future LST crazy-sessions of high volumes from two PL700 rebuilt Series Two's.

fm

P.S.

I hope for the best as my parents always said!!

fm